Functional properties of CD8+ T cells under lymphopenic conditions

A peripheral pool of T lymphocytes consists of several functionally distinct populations of CD8+ T cells. One of the major surface markers that allow to define different populations of T cells are CD44 and CD62L. Expression profile of these markers depends on the functional status of T lymphocyte. Naive CD8+ T cells express CD62L and do not express CD44 (CD62LhiCD44lo), clones of T cells activated during the primary immune response lose CD62L and express CD44 (CD62LloCD44hi). Central memory CD8+ T cells express both CD44 and CD62L (CD44hiCD62Lhi). However expression of activation markers not always correlate with an antigen experience of T cell. It is known, that in lymphopenic conditions peripheral T cells undergo homeostatic proliferation and acquire the memory like surface phenotype CD44hiCD62Lhi, but data about functional activity of these cells remain controversial. We studied relationship between surface expression of the markers CD44 and CD62L and functional properties of CD8+ T cells under lymphopenic conditions. We proved that surface expression of CD44 in not the only condition for T lymphocyte to acquire the functional properties of memory T-cells. It means that identification of CD8 + T-memory cells based solely on an expression profile of surface markers is not completely correct and requires confirmation by functional tests. Moreover, results of our research may become of practical importance for blood transfusion and bone marrow transplantation.